Keeling plots of dissolved organic carbon (DOC) concentration and Δ14C depth profiles imply rapid, diapycnal transport of DOC to the meso- and bathypelagic zones, but do not constrain the mechanism of redistribution. We review the 2-component Keeling plot model, and present an alternative formulation explicitly based on homogenization of water parcels. Applying this new model to DOC and dissolved inorganic carbon (DIC) depth profiles suggests that the dominant controls on DOC redistribution differ throughout the water column. DOC concentration and Δ14C gradients were consistent with biogeochemical processing in the epipelagic and advection in the mesopelagic. Vertical gradients in DOC concentration and Δ14C were insufficient for further interpretation in the bathypelagic. Ultimately, additional concurrent measurements of DOC and DIC concentrations and Δ14C values throughout the water column at more locations are needed to constrain the applicability of two-component mixing models to marine DOC.

Motivated by the need to develop clean, high purity preparative enrichments of individual compounds for micro-scale compound-specific natural abundance isotope and radiocarbon (C-14) analyses, we describe a new, two-dimensional, heart-cutting, low-bleed, three-oven, single GC preparative system, demonstrate its resolving capabilities as applied to a typically complex environmental sample matrix, and investigate the robustness with which it preserves the authigenic C-13/C-12 and C-14/C-12 ratios of individual compounds it targets for preparative enrichment. The system is comprised of a programmable temperature vaporizing (PTV) inlet, a single GC oven, two modular, door-mounted, resistively heated low thermal mass (LTM) columns, a preparative fraction collector (PFC), and a Deans pneumatic switching device which facilitates heart-cutting between the system's 1 degrees and 2 degrees chromatographic dimensions. Further, the system's inlet and trapping parameters are optimized for the efficient preparative enrichment of the methyl ether and ester derivatives of the lignin phenol compound class. The lignin phenols include such compounds as the vanillyl and syringyl aldehydes, ethanones, and acids and are unrivaled biomarkers of terrestrial organic matter, some of which are also important components of fragrances and flavors. Using this suite of compounds, the suitability of this augmented preparative capillary GC (PCGC) system was investigated for micro-scale compound-specific (CS) stable isotope and natural abundance radiocarbon analyses (RA). Analysis of a >300 injection enrichment scheme reveals the instrument to fractionate C-13 in predictable ways and to preserve the authigenic Delta C-14 of compounds it targets for preparative enrichment to within 6.7 +/- 5.0 parts per thousand, demonstrating the promising new utility of such systems towards micro-scale CSRA investigations for which clean and high resolution separation techniques are prerequisite. (C) 2011 Elsevier B.V. All rights reserved.